1. Field of the Invention
The invention relates to a mixture formation means for the reformer of a fuel cell system or for a heater with fuel feed, air feed and a mixture formation area.
2. Description of Related Art
Mixture formation means are always used when there must be mixing of the liquid or gas involved in the reaction before entering the reaction space. In particular, it is possible to set a defined mixing ratio. Another important task of mixture formation prior to entering the reaction space is to form an especially homogeneous mixture.
Fuel cell systems, particularly those for operation with liquid fuels such as gasoline or diesel fuel, require a reforming unit which converts a mixture of air and fuel vapor into a hydrogen-rich reformat with which the fuel cell is operated. Production of a homogeneous mixture of air and fuel vapor is a particular problem for diesel fuel due to the relatively high temperatures required for complete vaporization. The temperature for complete vaporization of diesel fuel is roughly 400° C. Conventional vaporization techniques often fail due to carbonization and inhomogenous mixture.
International Patent Application Publication WO 00/06948, the U.S. national phase of which is now U.S. Pat. No. 6,793,693 B1, discloses mixture formation using the “cold flame” principle. However, mixture formation devices which function using this principle are relatively large and are difficult to adjust in the load range. Conventional injection processes such as continuously operating pressure atomizers require permanently high injection pressures and therefore cannot be modulated over the required load range.
Economical injection systems for internal combustion engines are known in the form of pressure impulse injection means, for example, from published German Patent Application DE 41 06 015 A1 and its counterpart U.S. Pat. No. 5,540,206. These pressure impulse injection means are only moderately suited for use in reformers for fuel cell systems or for use in a heater since complete diesel vaporization and homogeneous mixture formation cannot be accomplished.